Gmat review question

[raunekk]

Hi guys..can anyone explain me this:

A certain clocks marks every hour by striking a number of times equal to the hour, and the time required for a stroke is exactly equal to the time interval between strokes.At 6:00 the time lapse between the beginning of the first stroke and the end of the last stroke is 22 seconds.At 12:00 ,how many seconds elapse between the beginning of the first stroke and the end of the last stroke?

a.72
b.50
c.48
d.46
e.44


thanks.

[onesome]

OA is D = 46

In explanation :
At 6 there were 6 strokes and 5 intervals between each stroke.
Lets say clock strikes like : tum (just a sound )
So at 6 it will be :
tum <interval>
tum <interval>
tum <interval>
tum <interval>
tum <interval>
tum

which is total of 6 tum and 5 interval.
Question says - time required for a stroke is exactly equal to the time interval between strokes.
So tum = interval
That is, we have 11 equal time intervals that took 22 seconds.
1 tum or interval = 2 seconds
Therefore at 12 : 12 tum and 11 interval = (2*12) + (2*11) = 24+ 22 = 46

I hope this helps..

[raunekk]

Hi onesome,
Thanks a ton.. but as u said..

Question says - time required for a stroke is exactly equal to the time interval between strokes.
So tum = interval
That is, we have 11 equal time intervals that took 22 seconds.
1 tum or interval = 2 seconds
Therefore at 12 : 12 tum and 11 interval = (2*12) + (2*11) = 24+ 22 = 46

CAn u please explain me..as to how 11 intervals in 12 seconds.. and how 1 interval=2 seconds..i am just not getting that...

thanks..

[cornell]

Hi Raunekk,

I just want to help to make it clear for you... you asked:

CAn u please explain me..as to how 11 intervals in 12 seconds.. and how 1 interval=2 seconds..i am just not getting that...

It was not 11 intervals in 12 seconds, but it is total 11 periods of "tums" and intervals. It is exactly like Onesome analogy :

tum <interval>
tum <interval>
tum <interval>
tum <interval>
tum <interval>
tum

from the analogy above we can see that at 6.00 there are 6 tums + 5 intervals = 11 periods of time. And 11 periods of time needs 22 seconds. Right?

So, we can simply find the time needed for 1 period, 22 seconds / 11 periods = 2 second / period.

Now, by the same analogy, if it is 12.00, so we will hear the tum 12 times right. So the analogy is:

tum <interval>
tum <interval>
tum <interval>
tum <interval>
tum <interval>
tum <interval>
tum <interval>
tum <interval>
tum <interval>
tum <interval>
tum <interval>
tum

We have 12 tums and 11 intervals --> 12 + 11 = 23 periods, right?
1 period needs 2 seconds, so in 23 periods we need exactly 23 periods x 2 seconds = 46 seconds (D)

I hope this helps...

Enjoy your day